U.S. Pat. No. 4,956,759; hereinafter referred to as "Philips" patent, discloses an illumination system which includes a light source, a pair of concave mirrors positioned to collect substantially all of the light from the source, and a non-imaging optic having an input aperture positioned to collect substantially all the light and re-direct it in a somewhat controlled manner.
The second concave mirror, as disclosed in the Philips patent, is of a geometry such that a linear geometry is prohibited. Since the second concave reflector is forming an image of the source at a point remote rather than proximate to the source, the centers of curvature of the concave mirrors and the source can at best exist in a co-planar format. Such a geometry is disadvantageous for several reasons: (1) This geometry requires the incorporation of larger packaging (envelope); (2) This geometry requires greater complexity of mechanics with corresponding greater costs; and, (3) as a result of its departure from a common centerline, this geometry exhibits greater sensitivity to alignment errors. The ability to produce illumination beams of low angular divergence, a direct function of the non-imaging optic, is to transform, by some factor, the angle at which light enters the input aperture to some lesser angle upon departure through the exit aperture. Generally, the greater the angle of divergence entering a non-imaging optic, the greater the angle exiting the non-imaging optic. The illuminating systems of the prior art produce angles as great as 90 degrees to the non-imaging optics centerline, entering the aperture. In contrast, the object of the geometry of the present invention is to allow for the rays of greatest divergence to enter the non-imaging optic at approximately 65 degrees; and, thus, to be much more efficient in the concentration of energy than the designs of the prior art.
Furthermore, an all spherical version of the design disclosed in the Philips patent, would result in the formation of an asymmetrical energy distribution at the entrance aperture of the non imaging optic. Additionally, fabrication of an all spherical version of the design disclosed in the Philips patent (with the second concave reflectors source and image positioned with minimal displacement and, correspondingly, minimal aberration) would be extremely difficult.
It is an object of this invention to provide an illumination system that is more efficient in concentrating energy than prior art systems.
Another object is to produce illumination beams of lower angular divergence than the prior art.
It is also an object of the present invention to provide a system that displays a relatively low sensitivity to alignment errors.
A further object of the invention is to provide a system wherein the envelope size is minimal compared to prior designs, and wherein the complexity of the mechanics is reduced with corresponding reduction in fabrication costs.
A still further object is to provide an illumination system which is adaptable to a wide variety of instruments which use a light source, including but not limited to microscopes, slide projectors, surgical instruments, spectrometers, ophthalmoscopes, and endoscopes.